1. Field of the Invention
This invention relates to a process for dewaxing petroleum oils and fractions thereof by selectively removing normal paraffinic and other undesirable hydrocarbons from petroleum oils in which they are present in admixture with other hydrocarbons, in order to lower the pour point of such oils. More particularly, the invention relates to an improved single-step process for selectivity removing normal paraffinic and other undesirable hydrocarbons from petroleum oils by contacting same with a specific zeolite catalyst in the presence of a large amount of co-fed water.
2. Description of the Prior Art
It is well known in the art to form various lubricating oils from hydrocarbon fractions derived from petroleum crudes. A heretofore practiced common procedure known in the art is to extract these hydrocarbon fractions with various solvents so as to give a raffinate of a desired high viscosity index, such material being resistant to changes in viscosity with changes in temperature and thus being useful under varying operating conditions. Moreover, it is particularly desired that the lube oil have a low pour point so that it can be effectively used at low temperature conditions, since excessive thickening at low temperature is often unacceptable. It is also known in the art to carry out dewaxing operations by contacting hydrocarbon fractions with crystalline aluminosilicate zeolites having pore sizes of about 5 Angstrom units so as to selectively remove normal paraffins.
The present invention is concerned with an improved process for dewaxing normal paraffin-containing oils which is more economical than conventional solvent dewaxing procedures or catalytic dewaxing procedures involving 5 Angstrom unit zeolites and which, with certain feedstocks, produces a higher product yield with equivalent or higher pour point reduction and prolonged catalyst cycle time between regenerations.
Trace amounts of water used to promote various catalytic reactions, not including gas oil dewaxing, is known in the art. For example, U.S. Pat. No. 3,546,100 teaches restricting the partial pressure of water in contact with a hydrocracking catalyst during hydrocracking of a hydrocarbon compound to within the range of 10 to 130 mm. U.S. Pat. No. 3,649,524 teaches a high temperature reforming process using only 8-20 ppm water.
Somewhat larger amounts of water have been used in high temperature catalytic dehydrogenation of hydrocarbons (U.S. Pat. No. 3,907,921), wherein 25-3000 ppm of water is used; and in hydrodesulfurization of gas oils and cycle oils (U.S. Pat. No. 3,720,602) wherein 5 to 50 percent of water is injected. In the latter patent, the catalyst material used does not include zeolite materials.
The use of large amounts of water, i.e. about 0.5 to about 15 moles water/mole hydrocarbon feedstock, would be expected, based upon the teaching of the art, to destroy conventional porous, siliceous heterogeneous catalysts, such as used in the present method.
U.S. Pat. No. 3,755,138 discloses a two-step process for dewaxing hydrocarbon oil feedstocks boiling above about 650.degree. F. having an intermediate pour point. One step of the patent process comprises solvent dewaxing and the other step comprises contact with a ZSM-5 type of zeolite in the absence of co-fed water. U.S. Pat. No. Re. 28,398 discloses dewaxing a hydrocarbon oil boiling above 350.degree. F. by shape selective cracking and hydrocracking over a zeolite of ZSM-5 type without co-fed water.